The invention concerns miniature x-ray tubes for therapeutic treatment of specific areas within the human body, such as a blood vessel, duct or other small lumen, and in particular the invention concerns cooling of such a miniature x-ray tube in an efficient manner without requiring an unduly large catheter to carry the coolant.
Miniature or small x-ray tubes for human therapeutic treatment are discussed in several prior patents, including U.S. Pat. Nos. 5,854,822, 5,621,780 and 6,319,188. Such small x-ray tubes have been intended for treatment of tumors within surgical openings in the body, for treatment within blood vessels using a catheter containing the tube, and for other radiation treatments within the body. Cooling of miniature x-ray tubes, particularly when used within lumens of the body, is an important issue. One prior approach has been an open loop cooling system, wherein a liquid coolant (saline solution) is dumped into the blood flow after flowing over the anode end of an x-ray tube. With such an open system heated saline solution can damage blood cells if heated beyond 43° C. Moreover, excessive flow of saline into the blood can be deleterious. Still further, an open loop system requires extra protective measures to assure sterility of the coolant liquid.
In other x-ray tube cooling arrangements, the blood itself has been used as a coolant. This is particularly risky because when the blood directly contacts the hot anode (or a structure directly in contact with the anode), the blood is almost certain to be overheated and to experience cell damage and cause thrombus to form.
There is a need for a miniature x-ray tube cooling system, particularly a closed loop cooling system, which effectively, reliably and efficiently cools a miniature x-ray tube without requiring an objectionable expansion of the size of the catheter carrying the tube.